Product and process of polymerizing ethylene



United States Patent PRODUCT AND PROCESS OF POLYMERIZING ETHYLENE ArthurW. Lat-char, Mendenhall, Pa., and Donald C. Pease, Wilmington, Del.,assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing. Application August 2, 1951, SerialNo. 240,044

6 Claims. (Cl. 260-94.9)

This invention relates to new macromolecular polymers of ethylene and tomethods for their preparation. The application is a continuation-in-partof copending application, S. N. 739,264, filed April 3, 1947, nowabandoned. Subject matter described and claimed herein was disclosed inapplicants copending continuation application, Serial Number 563,699,filed February 6, 1956, and now abandoned.

It is known that when ethylene is subjected to pressures in the range of500 to 3000 atmospheres, at temperatures of 100 to 300 C., itpolymerizes to products ranging from oily liquids to wax-like solids. Asgenerally produced, the wax-like solids melt in the range of 100 to 120C., have an average density of 0.925, an elongation at break of 550 to700%, a tensile strength on final crosssection of 16,000 lbs./in. astifiness modulus in the range of 16,000 to 21,000'lb./in. an amorphouscontent of the order of 22%, a degree of chain branching correspondingto about one side chain per 20 carbon atoms in the chain, and aninherent viscosity of 0.92 measured at 0.125% concentration in xylene at85 C. Although this represents a remarkable combination of properties,for many industrial uses they fall short of meeting even minimumrequirements.

It is also known that in the presence of specific catalysts, and undercertain conditions of temperature and pressure, carbon monoxide andhydrogen react to give methanol and branched chain higher alcohols (U.S. Patent 1,770,165). It is also well known that under certain otherconditions involving the use of certain cobalt-containing orrutheniumcontaining catalysts, the reaction between carbon monoxide andhydrogen leads to the formation of parafiin waxes (Fischer et al.,BrennstofE-Chemie 19, 226-30 (1938); ibid, 20, 247-50 (1939); cf. alsoBrit. 468,434).

High molecular weight straight chain alcohols and otheroxygen-containing organic compounds have also been obtained byhydrogenation of carbon monoxide in the presence of metals of the eighthgroup suspended in parafiin hydrocarbons (Patent Applications in theField of Fischer-Tropsch and Allied Reactions, vol. II, 1948, translatedby Charles A. Meyer & Co., containing the following German patentapplications of the I. G.: R-106,854 IVD/ 120, January, 1940; 0. Z.14,718 J/Z, April 25, 1944; 0. Z. 14,225, January 8, 1943; 0. Z. 14,226,June 8, 1943; O. Z. 12,880, July 5, 1941). In general, the waxespreviously obtained were produced simultaneously with compounds ofrelatively low molecular weight (Fischer and Pichler, Brennstolf Chemie20, 247-50 (1939)), the average molecular weight of the products beinggenerally less than 1000. These previously known waxy reaction productscontained ingredients which could be distilled at high temperatures andlow pressures (200 C./2 mm).

An object of this invention is to provide a process for the productionof new compositions of matter. Another object is to provide a newpolymer of ethylene having properties superior with respect toelongation and stiffness resulting, inter alia, from molecular structureand crystal- 2,816,833 Patented Dec. 17, 1957 hitherto known ethylenepolymer. These ethylene polymers melt in the range of 127 to 132 C.,have a stiffness modulus of from 137,000 to 215,000 1bs./in. ,.abreaking strength, based on the drawn dimensions, of 40,000 to 55,000lb./in. an elongation at break of 1200 to 1300%, a relative viscosity offrom 1.0 to 1.5, measured at 0.125% concentration in xylene at C., adegree of chain branching corresponding to less than one side chain per200 carbon atoms in the main polymer chain, and an amorphous content ofnot more than 10%.

The novel ethylene polymers of this invention are made by subjectingethylene to pressures of from about 5,000 to 20,000 atmospheres attemperatures above 45 C. but below 200 C., preferably in the presence ofa material which yields reactive free radicals under the conditions ofreaction.

In a preferred method for preparing the novel ethylene polymers of thisinvention, a pressure reactor is charged with a solvent, such as anaromatic, cycloaliphatic, or parafiinic hydrocarbon, or an alcohol, andfrom 0.01 to 1%, based on the charge, of a substance which yieldsreactive free radicals under the conditions of reaction, such as anorganic peroxy compound or azonitrile, the reactor is connected to asource of ethylene and pressured to the selected pressure with ethylene.The reactor is then closed and heated to between 45 and 200 C.,preferably to between 40 and 100 C., and the pressure within the reactormaintained by further compression. After the desired degree of reactionhas been attained, the reactor is allowed to cool to room temperature,opened, and the contents discharged. The polymer is then isolated byconventional methods. The polymers produced in accordance with theprocess of this invention have melting points ranging from 127 to 132 C.

Melting point is determined under a microscope having a micro-heatingstage provided with controlled means for heating films of polymer ofabout 100-300 microns in thickness to the fusion temperature. Themelting point is taken as the temperature at which there isdisappearance of double refraction.

The examples which follow are submitted to illustrate and not to limitthis invention.

Example 1.Eighty-nine parts of benzene, 0.425 part of2,2-azobis-2,4-dimethylvaleronitrile, and 78 parts of ethylene arecharged into a pressure vessel capable of withstanding internalpressures of at least 1000 atm. One end of the vessel is fitted with aneedle valve for admitting compressed ethylene, for example, at 1000atm., and the other end is fitted with a removable closure which makes atight seal when subjected to an internal pressure of several hundredpounds per sq. in. in excess of the external ressure, but which, whensubjected to an external pressure in excess of the internal pressure,transmits the higher pressure to the contents of the vessel. The closureconsists of a piston having a diameter slightly less than the bore ofthe vessel, attached to a shank of considerably smaller diameter. Whensubjected to internal pressure only, the piston is supported by a ringof compressible packing backed by a packing gland. The shank isunsupported and extends through a hole in the gland. This vessel,containing the reaction mixture previously described, is placed in alarger, heavy walled, heated cylinder containing glycerine as a pressuretransmitting fluid. Pressure is built up in this cylinder by means of ahydraulic intensifier and is maintained at 6500-7300 atm. for a periodof 66 hours, during which time the temperature is held at 45 C. Afterrelease of pressure and removal of benzene 11.8 parts of polymer isobtained. This polymer has a,

melting point of 130.3 C. and a density (annealed) of 0.956.

Example 2.Eighty six parts of benzene, 79 parts of ethylene... and 0.4.8part of, 1,L'-azodicyclohexanecarbonie trile are held for 68 hours at7300 atm. and 80 C. in.the' equipment described in Example 1.. The:product is dissqluedin hot xylene, thesolutionfiltereiand the polymerrecovered from the filtrate by. precipitating with methanol, filtering,and drying. Forty three; parts of: polymer are recovered. This materialhas a density (annealed). of 0.970 and a melting pointof 127.60. C. Thesame catalyst at 100. atm. pressure gives a polymer meltingat 122.4 C. I

Example. ifs-Eighty. six parts of benzene, 84 parts ofethylene, and 0.44part; of. ditertiary hutyl' perphthalatearelcharged into the.apparatusadescribedunder. Example 1 and maintained at 7300. atm. and 85C. for 1-9 hours; Thepolymer is dissolved in hot .xylene, thesolutionfiltered, and precipitated. with methanol. Nineteen. parts of polymer isobtained after filtration anddrying. Its melting: point is 128.0 C., ascomparedwith 120.3 C. forethylene polymer obtained with the samecatalyst at 1000 atm.

Example 4.4eventy five parts of tert.-buta-nol, 90 parts-of ethylene,and- 02 part of alpha,alpha--azodiiso+ butyronitrileare. heldfor- 17hours at 60: CL, undera pressure of 6700-7300atm. in the apparatusdescribed under Example 1'. Seventy partsof polymer are-obtained.

This polymer has a melting pointof- 131.0 C., a relativeviscosity of"1.15, measured at 0.125% concentration in xylene at 85' C; i

' Example 5.-The apparatus described iii-Example 1: is-

6900- 7300 atm. for a period of 18- hours, with water. as

the pressure transmitting medium. The temperature is 60* C. Fiftyfourparts of polymer are recovered by precipitating a hot xylene solution ofthe reaction product with methanol. This polymer melts at 132.l C. andhas a density (annealed) of 0.954. A film of the polymer obtainedbymoulding at a temperature above the melting pointhas an elongation atbreak of 1202% and a tensile strength, based on final dimensions, of54,700 1b./sq.in. The relative viscosity is 1.14, measured at 0.125%concentration in xylene at 85 C.

Example 6.Sixty,seven parts of isooctane, 8,1parts-of ethylene, and 0.2part of alpha,alpha azodiisobutyronitrile are subjected to a pressure of69007300 atm. for. 20 hours at 60' C. The polymer, 5. parts. of which isre.- covered in the same manner describedin the preceding example, has amelting point of 127.4 C.

Example 7.- The apparatusemployed in thepreceding examples is used to.hold 82' parts of methanol, 90 partsv or ethylene, and 0.2. part ofbenzoyl' peroxide under. a pressure of 6700 7300 atm. for 19. hours.Thetemperature is'maintained at 80 C. Twenty five parts. of poly.-. mer,having a melting point of 130.0 C., is-recovered by. the procedureoutlined in Example 2.

Example 8.In this exampleand in those which, follow, aheavy. walled,externally heated steel cylinder serves both. as acompression and.reaction chamber.. One. end

of the cylinder is fitted with a closure retaining high internal'pressures; the other with a packed plunger which.

is'forced into the bore of the cylinder by means ofasecondpiston oflarger cross section. The second piston is.hydraulically actuated. Asmall radial hole.v through the cylinder wall near the piston-end is vused to. compressed ethylene to the. chamber when the pistomposition is,at the start of the. compressionstroke. Irr opera;

tion, the high pressurepiston is lockedirr, this position;

after charging. with. the reaction medium-and catalyst,- and;

the, chamber is .filled with ethylene at 1.00.01 atm. The;-

reaction mixture, is then compressed flay-forcing theplnnger 4 into thechamber, the gas inlet port being sealed off by the advancing plunger.Two hundred fifty-eight parts of benzene, 1.25 parts ofalpha,alpha-azo-diisobutyronitrile and 300 parts of ethylene arecompressed to 7400 atm. in the apparatus described above and thecylinder heated to 60 C. As the pressure drops, due to polymerization ofthe ethylene, it is periodically raised to 7400 atm. by

' advancing the piston. The pressure range during the 19 hour reactionperiod is 5750. to 7400 atm. Seventy-nine parts. of polymer is.recovered bythe procedure employed in Example 2.

The polymer melts at 129.8 C. and has a density (annealed) of 0.955. Therelative viscosity of a 0.125% solution in xylene at C. is 1.127. A filmobtained by pressing the polymer between plates heated to C. isexceptionally stiff, having a modulus of 145,000 lb./sq. in. Its tensilestrength on initial dimensions is 2920 lb./sq. in., on final dimensions40,000 lb./sq. in.,-and its: elongation at break is-1240%.

The intensity of the infra-red absorption at 11.33;. in-' dicates thatside chains are present in the polymer atv a frequency of less than 1.side: chain per ZOO-carbon atoms in the, main chain and hence that thepolymer is highly linear in-- structure. An absence ofabsorption at5.71.0 indicate freedom from carbonyl groups.

Polymer made in benzene-in the-same equipment and with the sameinitiator but'a't a pressure 0119004000 atm. hasa melti-n'g point'of121t8 C.

Example 9.-.-Two hundredfifty-eight parts of benzene,

lt25fpartsof alphagalpha'-azodiisobutyronitrile, and 300* 400 partsofethylene are subjected to'a pressure of 7680 atm. in the apparatusdescribed" under Example 8. The temperature is-60 C. and'the-pressurerange over the 21 hour reaction period is 5700-7680 atm. One hundred andseventy-five parts of polymer melting at 130.6" C. is obtained. A filmpressed from the polymer between heated plates has astifiness'modulus of137,000'lb./ sq. in.,

atensile strengthof' 4400 lb'./sq. in; based on original dimensions.

Ecampl'e 1-1 '-Two hnndred'parts 'of absolute ethanol, IO'Opartsofwater, 0.3; part of'alpha;alpha' nzo'diisobutyros nitril'e; and 300parts o f ethyl'ene are compressed to'7880- atm: andheatedio 60 C. inthe apparatus described under Example 8; The'pressure is held between5040'and 7880 atm.- for 2'1hours. Onehundredforty'parts' of polymermelting at 129.8- C; is obtained: A very'strong film isobtainedbypressingthe polymer between heated plates. Its tensilestrength, basedon original dimensions, is 11,800 1b./sq. in. and it's'stitfness'modulus is 215,000 lb./sq. in.

Example 12:-One hundredseventy two parts oi benzene, 400 parts ofethylene, and 0.30 part of di(tertiary butyl) peroxide are chargedintoth'eapparatus described in Example 8, and maintained at 6'800'to7700'atmospheres pressure and 122 C. for 18' hours. Twenty-nine parts ofpolymer melting-at 12818". C; are obtained.

X-ray. data indicate that ethylene: polymers. obtained under pressuresof the order off7000atmospheres are, highly crystalline, havingamorphous contents, when measured by-the'metliod of Mathews et ahActaCrystalg lographica 2, 85' (1949), varying between-6 and 10%'-.

In place of-=the catalysts used in theexamples; there-- may be used anymaterial which yields reactive free radicals under the conditions ofreaction, Examples-are azoni-triles of the' typedisclosed and claimed inUi' Si dra zines, hydraziniumcompounds and' the like.

As a-rule; the proeess is operated in tliepresence of a solvent ordiluent but this is only optional, as the process can be carried out inthe absence of such solvent or diluent, provided provision is made forrapid dissipation of the high heat of reaction. Batch operations arepreferably conducted with good agitation to prevent nonuniformity ofheat removal and to insure uniformity of product quality. Although theexamples describe batch operations, the process of the invention can becarried out as a continuous operation. When so conducted, improvedresults can be obtained by taking a comparatively low yield per pass andby recycling the unconverted ethylene.

The most generally used pressures are in the range of 5,000 to 15,000atm.; this embodies the preferred operating pressure conditions.

The polymers of this invention have a higher degree of linearity thanany hitherto known ethylene polymers. This fundamental property isreflected in a higher melting point, higher density, greatercrystallinity, and greater stiffness. These polymers are freer fromchain branching and have a lower amorphous content than hitherto knownethylene polymers. These unique and distinguishing properties set thesepolymers aside from any hitherto known hydrocarbon polymers and areresponsible for their extraordinarily high tensile strength, stiflnessmodulus, and elongation characteristics.

We claim:

1. Solid polyethylene, exceptionally stiff, having an amorphous contentof not more than containing side chains, at a frequency of less than 1side chain per 200 carbon atoms in the main chain as determined byinfra-red absorption analysis, having a melting point above 127 C., atensile strength, based on original dimensions, between about 2900 andabout 11,800 pounds per square inch, a relative viscosity above 1.0 andup to about 1.5 measured at 0.125% concentration in xylene at 85 C., anda density (annealed) in the range of 0.95 to 0.97.

2. Solid polyethylene, exceptionally stifi, having an amorphous contentof not more than 10%, containing side chains, at a frequency of lessthan 1 side chain per 200 carbon atoms in the main chain as determinedby infra-red absorption analysis, having a melting point above 127 C., arelative viscosity between 1.127 and about 1.5 measured at 0.125%concentration in xylene at 85 C., and a density (annealed) in the rangeof 0.95 to 0.97.

3. In a process for the preparation of solid homopolymers of ethylene,the step which comprises conducting the polymerization at a pressure inthe range of 5,000 to 20,000 atmospheres and a temperature between C.and 200 C. in the presence of a catalyst selected from the group of azocompounds, peroxides, amine oxides, hydrazines, and hydraziniumcompounds.

4. In the polymerization of ethylene to solid homo! polymers at 45 C. to100 C. in the presence of catalysts effective therefor, the step whichcomprises effecting said polymerization at a pressure between 5,000 and20,000 atmospheres.

5. In a process for the preparation of solid homopolymers of ethylene,the step which comprises conducting the polymerization at a pressure ofabout 7,000 atmospheres, at a temperature between 45 and C. and in thepresence of a catalyst selected from the group consisting of2,2'-azobis-2,4-dimethylvaleronitrile; 1,1-azodicyclohexanecarbonitrileand alpha,alpha-azodiis0butyronitrile.

6. In a process for the preparation of solid homopolymers of ethylene,the step which comprises conducting the polymerization at a pressurebetween 5,000 and 20,000 atmospheres and at a temperature between 45 C.and 200 C. in the presence of free radical generating polymerizationcatalysts selected from the group consisting of2,2'-azobis-2,4-dimethylvaleronitrile; 1,1-azodicyclohexanecarbonitrileand alpha,alpha'-azodiisobutyronitrile.

References Cited in the file of this patent UNITED STATES PATENTS1,952,116 Bridgman et a1 Mar. 27, 1934 2,153,553 Fawcett et al. Apr. 11,1939 2,352,328 Kleine June 27, 1944 OTHER REFERENCES Cross at al.:Discussions Faraday Soc., No. 9, 235-45 (1950).

Richards: Plastics, pp. 288-289 (Oct.-Nov.-Dec. 1950).

Bryant: J. Polym. Sci., 6, 547, 550, 555 (1951).

Richards: J. Appl. Chem. 1, August 1951, pp. 3704176.

Gourlay et al.: British Plastics, vol. 29, pp. 446-45l (1956).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No)2,816,883 I December 17, 1957 Arthur W, Larchar et a1, 7

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 3, line 11, for "127.60 0.," read 12756 0.; line 12, for "100atm," read --1000 atm.-.

Signed and sealed this 18th day of February 1958 Attest:

KARL H, AXLINE Conmissioner of Patents

1. SOLID POLYETHYLENE EXCEPTIONALLY STIFF, HAVING AN AMORPHOUS CONTENTOF NOT MORE THAN 10%, CONTAINING SIDE CHAINS, AT A FREQUENCY OF LESSTHAN 1 SIDE CHAIN PER 200 CARBON ATOMS IN THE MAIN CHAIN AS DETERMINEDBY INFRA-RED ABSORPTION ANALYSIS, HAVING A MELTING POINT ABOVE 127*C., ATENSILE STRENGTH BASED ON ORIGINAL DIMENSIONS, BETWEEN ABOUT 2900 ANDABOUT 11,800 POUNDS PER SQUARE INCH, A RELATIVE VISCOSITY ABOVE 1.0 ANDUP TO ABOUT 1.5 MEASURED AT 0.125% CONCENTRATION IN XYLENE AT 85*C., ANDA DENSITY (ANNEALED) IN THE RANGE OF 0.95 TO 0.97.
 3. IN A PROCESS FORTHE PREPARATION OF SOLID HOMOPOLYMERS OF ETHYLENE, THE STEP WHICHCOMPRISES CONDUCT ING THE POLYMERIZATION AT A PRESSURE IN THE RANGE OF5,000 TO 20,000 ATMOSPHERES AND A TEMPERATURES BETWEEN 45*C. AND 200*C.IN THE PRESENCE OF A CATALYST SELECTED FROM THE GROUP OF AZO COMPOUNDS,PEROXIDES, AMINE OXIDES, HYDRAZINES AND HYDRAZINIUM COMPOUNDS